Sensitivity of microwave emission to snow parameters: a model simulation study Marco Brogioni 1 , Paolo Pampaloni 1,2 1 Institute of Applied Physics – IFAC-CNR, Via Madonna del piano 10, 50019 Sesto Fiorentino (FI), Italy ph. 0039-055-5226432, fax. 0039-055-5226434, m.brogioni@ifac.cnr.it 2 Centro Telerilevamento a Microonde – CETEM, Via Madonna del piano 10, 50019 Sesto Fiorentino (FI), Italy ph. 0039-055-5226462, fax. 0039-055-5226434, p.pampaloni@ifac.cnr.it Abstract Snow cover is an important component of the hydrological cycle and a key indicator of global warming. Microwave radiometry has proved to be an important method to monitor this quantity. This work aims at investigating the sensitivity of microwave emission to snow parameters by means of an advanced model called IRIDE (Ifac RadiatIve Dry snow Emission). The model is obtained by properly coupling the Advanced Integral Equation Method and the Dense Media Radiative Transfer Theory under the Quasi-Crystalline Approximation. In the implementing of the model several errors found in literature have been corrected. 1.Introduction Snow cover has the largest area extent of any component of the cryosphere and has a significant impact on the global climate, on climate response to global changes and as a key indicator of them. Remote sensing of snow is traditionally carried out mostly by using optical sensors. However, the operability of these instruments strongly depends on weather conditions whereas microwave sensors operating in appropriate frequency bands are almost insensitive to the weather phenomena. The sensitivity of microwave emission to snow type and water equivalent (SWE) has been investigated in several theoretical and experimental studies, which demonstrated the potential of microwave radiometry in monitoring snow parameters and seasonal variations in snow cover. To analyze experimental data and understand the interaction between electromagnetic (e.m.) waves and targets, models describing the emission and scattering must be used. The theoretical models are based on the electromagnetic theory and are the most complex and rigorous. In order to accurately describe the e.m. behavior of a snowpack, surface scattering from soil and volume scattering from snow must be combined in an appropriate model. In this work we used the Advanced Integral Equation Method (AIEM) to describe the scattering from soil [1] and the Dense Medium Radiative Transfer Theory under the Quasi-Crystalline Approximation (DMRT-QCA) [2] to simulate the volume scattering of snow. These models have been selected because are among the most advanced and can simulate the e.m. behavior of a soil covered by snow over a wide spectrum. 2. Model description This work was addressed to study how the snow parameters affect the electromagnetic emission of Alpine dry snow covers by means of an advanced model called IRIDE (Ifac RadiatIve Dry snow Emission model) developed at IFAC-CNR. The model is based on coupling of the AIEM and the DMRT-QCA. The first model has been chosen due to its wide validity range and flexibility. On the other hand the DMRT-QCA can account for a wide range of particle sizes and for the adhesive properties of the ice crystals. To simulate surface scattering in the whole upper half space a bistatic polarimetric version of the AIEM has been developed, implemented and validated with numerical and experimental data. In the AIEM, the normalized scattering coefficient for the single scattering term is: ) , ( ! 2 ) ( ) ( ) ( ) ( ) ( 2 1 2 ) ( 2 1 2 2 2 y sy x sx n n qp n n k k qp c qp kc qp k qp o k k k k W I n e k S S S S sz z - - ⋅ = + + = ∑ ∞ = + - σ σ σ σ σ σ (1) where σ is the height standard deviation (HStdD) of the surface roughness and W (n) is the Fourier transform of the nth power of the surface auto correlation function (ACF). The transmitted polarization is p and q is the received one.